/*
 * Copyright (C) 2015 Jared Boone, ShareBrained Technology, Inc.
 *
 * This file is part of PortaPack.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#include "matched_filter.hpp"

#include <algorithm>
#include <cmath>

#include "utility.hpp"

namespace dsp {
namespace matched_filter {

void MatchedFilter::configure(
    const tap_t* const taps,
    const size_t taps_count,
    const size_t decimation_factor) {
    samples_ = std::make_unique<samples_t>(taps_count);
    taps_reversed_ = std::make_unique<taps_t>(taps_count);
    taps_count_ = taps_count;
    decimation_factor_ = decimation_factor;
    output = 0;
    std::reverse_copy(&taps[0], &taps[taps_count], &taps_reversed_[0]);
}

bool MatchedFilter::execute_once(
    const sample_t input) {
    samples_[taps_count_ - decimation_factor_ + decimation_phase] = input;

    advance_decimation_phase();
    if (is_new_decimation_cycle()) {
        float sr_tr = 0.0f;
        float si_tr = 0.0f;
        float si_ti = 0.0f;
        float sr_ti = 0.0f;
        for (size_t n = 0; n < taps_count_; n++) {
            const auto sample = samples_[n];
            const auto tap = taps_reversed_[n];

            sr_tr += sample.real() * tap.real();
            si_ti += sample.imag() * tap.imag();
            si_tr += sample.imag() * tap.real();
            sr_ti += sample.real() * tap.imag();
        }

        // N: complex multiple of samples and taps (conjugate, tap.i negated).
        // P: complex multiply of samples and taps.
        const auto r_n = sr_tr + si_ti;
        const auto r_p = sr_tr - si_ti;
        const auto i_n = si_tr - sr_ti;
        const auto i_p = si_tr + sr_ti;

        const auto mag_n = std::sqrt(r_n * r_n + i_n * i_n);
        const auto mag_p = std::sqrt(r_p * r_p + i_p * i_p);
        const auto diff = mag_p - mag_n;
        output = diff;

        shift_by_decimation_factor();
        return true;
    } else {
        return false;
    }
}

void MatchedFilter::shift_by_decimation_factor() {
    const sample_t* s = &samples_[decimation_factor_];
    sample_t* t = &samples_[0];

    const size_t unroll_factor = 4;
    size_t shift_count = (taps_count_ - decimation_factor_) / unroll_factor;
    while (shift_count > 0) {
        *t++ = *s++;
        *t++ = *s++;
        *t++ = *s++;
        *t++ = *s++;
        shift_count--;
    }

    shift_count = (taps_count_ - decimation_factor_) % unroll_factor;
    while (shift_count > 0) {
        *t++ = *s++;
        shift_count--;
    }
}

} /* namespace matched_filter */
} /* namespace dsp */
